Jaroslav Bohdan Rudnyckyj was born on November 28, 1910 in Peremyshl, Ukraine (now Poland). He was married to Maryna Rudnytska.
Rudnyckyj graduated in Slavic studies from Lviv University in 1937. He became research associate of the Ukrainian Scientific Institute in Berlin (1938–40). Later he taught at the Ukrainian Free University in Prague and Munich, at Prague University (1941–45) and Heidelberg University (1947–48). After his immigration to Canada in 1949, Rudnyckyi became head of the department of Slavic studies at the University of Manitoba in Winnipeg, where he stayed until his retirement in 1977. From 1955 to 1970, he served as president of the Ukrainian Free Academy of Sciences in Winnipeg, Manitoba. Rudnyckyj was member of the Canadian Royal Commission on Bilingualism and Biculturalism, which operated from 1963 to 1971. Furthermore, he was president of various associations, as the Canadian Linguistic Association (1958–60), the Canadian Association of Slavists (1959), and more. He was founding editor of Slavistica (1948), Onomastica (1951), Ukrainica Canadiana (1953–73), Ukrainica Occidentalia (1956–66), and Slovo na storozhi (1964–89). His numerous articles on Ukrainian language, onomastics, folklore, and literature have appeared in various periodicals, and many of his works have been separately published. After his retirement in 1977, Rudnyckyj moved to Montreal, Quebec. In 1992, he was made an Officer of the Order of Canada. Rudnyckyj died in Montreal on October 19, 1995.